erasure.scala

sealed trait Literal extends Term {

  def asOpt[A <: Literal](): Option[A] = {
    this match {
      case x: A => Some(x)
      case _ => None
    }
  }
}

abstract type pattern A is unchecked since it is eliminated by erasure
[warn] case x: A => Some(x)

trait Literal {
  def asOpt[A : LiteralCast](): Option[A] = implicitly[LiteralCast[A]].asOpt(this)
}
case class LiteralString(str: String) extends Literal
trait LiteralCast[A] {
  def asOpt(lit: Literal): Option[A]
}

implicit object LiteralStringCast extends LiteralCast[LiteralString] {
  def asOpt(lit: Literal): Option[LiteralString] = lit match {
    case l:LiteralString => Some(l)
    case _ => None
  }
}